1. Field of the Invention
The present invention relates to an undercoating composition and more particularly to an undercoating composition which has good application property and provides a coating film of low density having good resistance to corrosion, chipping, and secondary run. It will be used for automotive floor undercoating.
2. Description of the Prior Art
The conventional automotive undercoating is required to have, good rust preventing performance at high temperatures or at low temperatures near the exhaust pipes, and good chipping resistance at low temperatures and good run resistance at high temperatures. There are known some undercoating compositions which satisfy these requirements. They are composed of wax, asphalt, metal sulfonate, and inorganic powder (such as talc and calcium carbonate) which are dispersed in an organic solvent (such as mineral spirit). For example, Japanese Patent Laid open No. 189475/1988 discloses one which is composed of asphalt, metal salt of petroleum sulfonate, metal salt of petrolactum oxide, waxy substance, microcrystalline wax, metal salt of lanolin fatty acid, metal salt of synthetic sulfonic acid, and extender pigment (such as barium sulfate). Japanese Patent Laid-open No. 111382/1986 also discloses one which contains a sulfonate of an ultrabasic alkaline earth metal and petrolactum oxide dispersed in an organic solvent.
The conventional compositions mentioned above do not satisfy all of the requirements--corrosion resistance, chipping resistance, coating property, and resistance to secondary run. In addition, their large content of inorganic powder leads to unsatisfactory corrosion resistance when they are used in the form a thin film as the automotive floor undercoating. They also suffer from a disadvantage of forming a coating film of high density which adds to the weight of the automobile. Another disadvantage is poor atomization due to tailing at the time of spray coating.